Default Prophet (M600) or HTC TyTN, which one should I buy.

I just sold my XDA IIi, now I realy prefer smaller size like M600, it only £30/M for a 12 month contract, of course the phone is free, but many people said the cpu is too slow. acutally I want to use it as a gps..
should I go for the HTC TyTN? Does it realy gonna put in my pocket??